Educational or scientific device.



No. 774,998. PATENTED NOV. 15, 1904. I

R. w.- WILLSON. EDUGATIONAL 0R SCIENTIFIC DEVICE.

APPLICATION FILED JULY 1, 1904.

OOOOOO L.

Patented November 15, 1904.

PATENT OFFICE.

ROBERT W. WILLSON, OF CAMBRIDGE, MASSACHUSETTS.

EDUCATIONAL OR SCIENTIFIC DEVICE.-

SPECIFICATION forming part of Letters Patent No. 774,998, dated November15, 1904. Application filed July 1, 1904. Serial No. 214,869- (Nomodel.)

1'0 all whom it may concern:

Be it known that I, ROBERT W. WILLSON, of

Cambridge, in the county of Middlesex and State of Massachusetts, haveinvented a new and useful Improvement in Educational or ScientificDevices, of which the following,

tific devices adapted to teaching or demonstrating the principles ofastronomy or spherical geometry; and it consists in a portion of a thinspherical shell, preferably of transparent material, bounded in part bygreat circles at convenient angles to each other and adapted to fitclosely the curvature of a spherical surface upon which it is applied inuse. It is also suitably graduated and may thus be used for measuringdistances or angles on a spherical surface in the same manner as ascale, protractor, or straight-edge is used upon a plane surface, thebounding edges serving as guides for a pen or pencil.

In making drawings and geometrical figures on a spherical surface thearcs of great circles exercise the same functions as straight lines indrawings or diagrams on a plane surface. At present no suitableinstrument exists for drawing diagrams on a spherical surface such asmust be used in demonstration of the principles of spherical geometry.The only instruments now in use for such purposes are the compasses ordividers, and to draw the shortest line between two points on a sphererequires several operations with the dividers. In order to simplify andexpedite operations of this nature, I have invented my improvedspherical measure and ruler, by which such a line may be drawn as easilyas the straight line joining two points on a plane may be drawn by astraight-edge. It also serves to lay off a right angle on the sphere asthe T- square and triangle serve in the plane and to measure and lay offangles or distances on the sphere as the protractor or scale serves inthe plane. It may also be used with dividers to hold the point or centerinany desired location.

I preferably use my spherical measure or .rule in combination with asuitable spherical ing it desirable lightness as well as furnish-- ing aconvenient shape for grasping it firmly.

Referring to the accompanying drawings, wherein like letters representlike parts, Figure 1 shows an elevation of a hemisphere provided with myimproved spherical measure and ruler. Fig. 2 shows a plan of same. Fig.3 shows a section of the hemispherical shell with which is used myimproved spherical measure and ruler. Fig. 4 is an elevation of myimproved spherical measure and ruler detached from the spherical surfaceon which it is used.

In the drawings, A is my improved spherical measure and ruler,consisting of a thin preferably transparent shell, having the suit ablegraduations a a and bounded by the edges 6& a a, which form greatcircles of the spherical surface B, on which the shell A closely fits.The spherical surface B, I preferably form by the outside surface of athick hemispherical shell C, as shown in Fig. 3.

It will be observed that when the hemispherical surface rests on a planewith one of the edges a of the spherical ruler also resting on the planethe ruler may be moved about the hemisphere, and as long as the edge arests on the plane the other two edges a and a will make right angleswith the plane in the same way that a T-square always makes right angleswith the edge of the drawing-board with which it is used. Further, itwill be observed that in whatever position on the surface B the shell Ais placed its edges (4 a a will always describe great circles on thesurface B the same as a straight-edge always makes straight lines on aplane surface. Further, it may be observed that the graduated are a maybe centered upon the vertex of an angle on the spherical surface B, sothat the angles may be measured or determinate angles laid off by theuse of one edge of the spherical protractor or ruler as a guide for thepencil in a manner similar to the use of a protractor on a planesurface.

I claim 1. In an educational or scientific device a spherical surface incombination with a portion of a spherical shell conforming closely tothe curvature of the said spherical surface and adapted to be used fordiagrams or measurements thereon substantially as described.

2. In an educational or scientific device a hollow hemisphere having aspherical surface adapted for the use of pencil and eraser incombination with a portion of a spherical shell conforming closely tothe curvature of the said spherical surface and adapted to be used as aruler or measure thereon substantially as described.

3. In an educational or scientific device a hemispherical shell, havingan outer surface adapted for the use of pencil and eraser and an innersurface of convenient shape for grasping it firmly in combination withsuitable means for making diagrams or measurements upon said outerspherical surface substantially as described.

4:. In an educational or scientific device a spherical ruler comprisinga portion of a spherical shell, bounded in part by great circles atconvenient angles to each other, in combination with a spherical surfaceof the same curvature as the inner surface of the said spherical ruler,substantially as described.-

5. In an educational or scientific device, a spherical scale orprotractor comprisinga portion of a spherical shell provided withsuitable graduations in combination with a spherical surface of similarcurvature substantially as described.

6. In an educational or scientific device a spherical ruler and measurecomprising a portion of a spherical shell, bounded in part by greatcircles at convenient angles to each other and provided with suitablegraduation in combination with a spherical surface of similar curvaturesubstantially as described.

7. In an educational or scientific device, the portion A of a sphericalshell having the graduations a and a, and the edges a a and a formed bygreat circles in combination with the spherical surface B, substantiallyas described.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, on this 23d day of June,

ROBERT W. WILLSON. Witnesses:

A. H. FLANNERY, FRED JoY.

